Cocoa Pebbles Cereal Cake

Thick Cocoa Pebbles Chocolate Cake Layers frosted in Cocoa Pebbles Buttercream and covered in all the Cocoa Pebbles Cereal!

1 cup buttermilk room temperature
1 cup cocoa pebbles cereal, divided
2/3 cup sour cream room temperature
3 whole large eggs room temperature
1/3 cup vegetable oil
1 Tablespoon vanilla
1 15.25oz (or similar) Devils Food Cake Box Mix I prefer Duncan Hines, but any other brand will be similar

1 1/2 cups (or three sticks) unsalted butter Left out at room temperature for 10 minutes
1 pinch salt
1 Tablespoon pure vanilla
1/4 cup heavy cream
1/2 cup crushed cocoa pebbles cereal powder Start with 1- 1 1/2 CUP in the food processor, pulse to a powder, then measure out 1/2 cup.
1 cup cocoa pebbles cereal (whole)
7 cups powdered sugar

Preheat the oven to 325 degrees convection bake (if you're using convention bake ovens, you'll need to bake your cakes a little longer is all). Prep three 6" cake rounds with a swipe of shortening and dust of flour to prevent sticking. Set aside.
In a medium bowl, stir together the buttermilk and 1/2 cup of the cocoa pebbles cereal for about 20 minutes (this is great to do while waiting for the buttermilk to come to room temperature before baking anyway).
In a large bowl, hand-whisk together the buttermilk-cereal-soak-mixture, sour cream, eggs, oil, and vanilla until thoroughly combined. Toss in the other 1/2 cup of the cocoa pebbles cereal, and then sift in the devils food cake mix. Gently stir until just combined.
Split the cake batter between prepared cake rounds and bake for 25-27 minutes. After cooling in the pan for less than a minute, flip out the cake rounds onto a wire rack to cool completely. Wrap up with plastic wrap and freeze until you're ready to assemble. It's much easier to assemble with chilled or partially frozen cake layers.

In a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy. Add in the salt, vanilla, and heavy cream. Whip up again and then scrape down the sides of the mixing bowl.
Add in the cocoa pebbles cereal powder and the whole cocoa pebbles. If you're planning on piping with this buttercream (I didn't for this particular cake), you'll need all the cocoa pebbles cereal to be a powder so that the buttercream can fit through the piping tip. If not, follow the recipe here as instructed.
Slowly add in the powdered sugar 1/2 cup at a time and on low mixer speed. Add in a touch more heavy cream if needed, then flip the mixer on the highest speed. Let the buttercream whip up for about 2 minutes until it's lighter and fluffier in texture and color.

Tape a 6" cardboard cake round to an 8" one and place them on a cake turntable.
Add on a little bit of buttercream in the center of the cardboard round, then spread it out slightly with an angled icing spatula. Place down the first cake layer. Spread on about 1 cup of buttercream, then add on the next cake layer. Repeat.
Crumb coat the cake, then freeze for about 3 minutes to set.
With a straight icing spatula, spread on a thick layer of buttercream on the outside and top of the cake; smoothing it out with a straight cake scraper for smooth sides. Tip: This buttercream has little pieces of cocoa cereal throughout, so a gentle touch is needed to make them flush with the side of the cake. If you notice the pieces dragging and creating indents along the side of the cake, either remove the pesky piece, or use a more gentle touch when going around the cake. Leave the top unfinished for a more rustic look.
Next, place the cake onto a cookie sheet, and hand-press on the cocoa pebbles cereal onto the sides of the cake and on top.